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Biomedical subjects

J W Hand

Publications and source records attributed to J W Hand.

At least 37 records · Page 2Linked to original sources
PubMed1990

Treatment of functional menorrhagia by radiofrequency-induced thermal endometrial ablation.

42 patients were enrolled in a trial of radiofrequency-induced thermal endometrial ablation for the treatment of functional menorrhagia. The radiofrequency electromagnetic energy was delivered via a probe placed within the endometrial cavity. 10 patients received 330 kJ of energy, 10 received 445 kJ, and the other 22 received 660 kJ. 19 (87%) of those receiving the highest dose became amenorrheic or had a considerable reduction in menstrual flow. The procedure is simple and the heat induced in the endometrium does not penetrate much beyond the inner layers of the myometrium. There is no need for distension of the uterine cavity with flushing media.

Adult↗
PubMed1990

Use of Gaussian beam model in predicting SAR distributions from current sheet applicators.

The Gaussian beam model is shown to be a good predictor of SAR distributions due to current sheet applicators (CSAs). It is fast, efficient and adaptable. SAR distributions from a single applicator and from simple arrays of CSAs in homogeneous and layered lossy media are computed at 434 and 450 MHz at CPU times of less than 60 s. The good agreement between theory and experiment justifies the use of the Gaussian beam model to predict SAR distributions from CSAs.

Computer Simulation↗
PubMed1987

Heat delivery and thermometry in clinical hyperthermia.

This chapter has discussed some recent technical developments and trends in clinical hyperthermia. Several techniques for the treatment of tumours within 3-4 cm of the body surfaces were described. Each technique has its minor advantages and disadvantages; all techniques employing a single applicator produce temperature distributions with considerable gradients. The introduction of microwave and ultrasound techniques using multiple applicators in which there is some control of the pattern of the energy deposition within the treatment area should improve superficial treatments in this respect. A number of electromagnetic devices for regional hyperthermia are being developed and evaluated. The theoretical predictions of their performances are beginning to suggest restrictions to their use; the limited clinical experience is in general agreement with these predictions. Scanned and focussed ultrasound beams may offer the unique possibility of non-invasive, deep, yet localised hyperthermia in some locations. Such systems are at an early stage of their development; if they prove successful, their controlled and safe use will require detailed information of the temperature distributions produced. Invasive methods for inducing hyperthermia can produce relatively good temperature distributions. The development of 'constant temperature seeds' is promising. Both RF and microwave interstitial systems offering individual control of power to several channels should lead to improved temperature distributions. In general, non-invasive thermometry in clinical hyperthermia remains a distant goal, although developments in microwave radiometry may lead to systems with suitable spatial, temporal and temperature resolutions for use in superficial treatments. Invasive thermometry techniques can provide temperature measurements from several points or from along tracks within the treatment volume. The development of computer models to infer temperature distributions from the limited information available will be a major step in quantifying hyperthermal treatments.

Humans↗
PubMed1985

Effect of various regimens of chronic and acute nicotine exposure on myocardial infarct size in the dog.

Smoking is a risk factor for atherosclerotic coronary heart disease, and the risk increases with increasing numbers of cigarettes smoked. The effect of cigarette smoking on the size of acute myocardial infarction (AMI) has not been evaluated. This study describes the effect of 1 component of tobacco smoke, nicotine, on the size of experimentally induced AMI in closed-chest dogs. Daily exposure to nicotine before AMI increased the volume of infarcted tissue (p less than 0.0001). Acute exposure to nicotine (with prior chronic exposure) resulted in a larger volume of infarcted tissue (p less than 0.0001). Thus, chronic, acute and post-AMI exposure to nicotine has an adverse effect on the volume of subsequent infarcted tissue, and continued exposure after AMI further enlarges infarct size.

Animals↗
PubMed1985

Investigation of thermotolerance in mouse testis.

The effect of a two-fraction heat treatment on mouse testis has been assessed by measuring testis weight loss at 1 week after treatment. The rate of repair of 'sublethal' heat damage following the first treatment was dependent on the severity of the treatment. Using a primary treatment of 41.5 degrees C for 30 min, the weight loss following a test treatment of 41.5 degrees C for 30 min returned to that of the test treatment alone within an interval of 16-24 h. Using a milder primary treatment of 40.0 degrees C for 30 min, repair of sublethal heat damage appeared to be complete by 1-2 h. When a single test treatment was used, there was no evidence of heat-induced thermal resistance (thermotolerance) following primary treatments of 40.0 or 41.5 degrees C for 30 min, for periods up to 24 h between treatments. A small degree of thermotolerance could, however, be demonstrated following the most severe primary treatment used if full dose: effect curves were obtained. Thermotolerance, manifest as a decrease in slope, was maximal at approximately 4 h after the primary treatment. The results are discussed with reference to other normal tissue data.

Animals↗
PubMed1982

Considerations of radiofrequency induction heating for localised hyperthermia.

A finite difference technique for studying both spatial and temporal variations in temperature in tissues subjected to local hyperthermia is described. The calculation offers speed and simplicity whilst remaining stable. Its form is discussed in both 3-dimensional Cartesian coordinates and cylindrical coordinates. The technique is used to predict RF induction heating of a plane skin-fat-muscle model. Physical and physiological parameters are incorporated. These include the contributions to heating from both E and H fields associated with a plane coil, heat transfer across the skin surface for various environmental conditions, and an appropriate dependence of blood flow on temperature for each tissue layer. The effects on tissue temperature of varying each of a number of parameters in the model are considered.

Diathermy↗
PubMed1982

Temperature distribution in tissues subjected to local hyperthermia by RF induction heating.

We have used a finite difference formulation of the bio-heat transfer equation to predict temperature distributions in and around a non-uniformly perfused volume located in layered tissue. Using available data on blood flow in experimental tumours we have shown that techniques capable of highly localized heating are required to treat small, well perfused tumours effectively. However, the r.f. technique considered here produces acceptable temperature distributions in larger tumours with poorly perfused centres. Skin cooling improves the effective penetration of the hyperthermal treatment and may improve the uniformity of heating. However, the considerable heat flux through superficial tissues associated with chilled water cooling can produce large temperature gradients in such regions.

Energy Transfer↗
PubMed1982

Physical techniques for delivering microwave energy to tissues.

Some of the physical aspects of delivering microwave energy to tissues have been discussed. Effective penetration of a few cm may be achieved with external applicators whilst small coaxial or cylindrical devices can induce localized heating in sites accessible to catheters or to direct invasion. To heat deep tissue sites in general, systems of greater complexity involving a number of applicators with particular phase relationships between them are required. The problems of thermometry in the presence of electromagnetic fields fall outside the scope of this article. Their solution, however, is no less important to the future of clinical hyperthermia than the development of heating techniques. Finally, it should be remembered that physiological parameters such as blood flow have appreciable effects in determining the efficacy of the physical techniques described above.

Humans↗
PubMed1979

Effects of hyperthermia on the mouse testis and its response to X-rays, as assayed by weight loss.

The effects of both hyperthermia alone and X-rays combined with hyperthermia on mouse testis have been investigated. Testis weight on heating time was observed for temperatures in the range 39.5 to 43.75 degrees C. The relationship between the reaction rate and the reciprocal of absolute temperature indicated that, over the temperature range considered, the activation energy associated with such thermal damage was (646 +/- 45) x 10(3) J mol-1. No evidence was obtained to indicate a change in slope of the Arrhenius plot over this temperature range. Finally, despite the high sensitivity of the testis to heat and X-rays, no thermal enhancement of the weight loss after irradiation was observed when thermal treatments which, if given alone would produce some observable damage, were administered immediately after irradiation.

Animals↗